Previously, a variety of techniques and apparatus have been used to manipulate tissue in body cavities, generally for the purposes of surgical intervention or biopsy sampling for diagnostic purposes. Generally, the apparatus are designed for particular applications and their configurations are specially arranged for such applications. However, such techniques and apparatus generally suffer from numerous drawbacks.
For example, arthroscopic surgery often requires a number of separate incisions for the insertion of separate devices for expanding the joint, manipulating the tissue, and observing the surgical technique.
In other applications, such as biopsy sampling or surgical manipulation of soft tissue, devices are known which require specialized cutting or sampling surfaces, which often cannot be completely shielded to prevent inadvertent harm to surrounding tissue.
It is therefore considered desirable to provide a surgical method and instrument which provides for the insertion of a single probe into a body cavity and the manipulation of selected tissue under continuous observation. It is also considered desirable to provide a means for shielding the working surface of the instrument, thereby avoiding inadvertent injury to surrounding tissue.
There are other potential applications for which no surgical techniques or apparatus have yet been devised for performing the surgical manipulation within the body cavity. Consequently, the tissue of interest is ordinarily exposed by means of dissection, with the attendant increase in post-operative pain and morbidity. Exemplary of such an application is the surgical technique employed to relieve carpal tunnel syndrome.
The carpal tunnel is formed by an arch of the eight wrist bones, spanned on its palmar surface by the transverse carpal ligament, the flexor retinaculum. The carpal tunnel functions as a large mechanical pulley to provide the appropriate moment arms for the digital flexor tendons as they pass through the tunnel. The tendons can then transmit force out into the fingers and impart only an appropriate amount of tension to develop torque at the level of the wrist.
Within the carpal tunnel, these tendons are lubricated and nourished by two synovial membranes--the radial and the ulnar bursa. The median nerve also shares the carpal tunnel, then branches out to provide sensory innervation to the palmar surfaces of the thumb, index, long and a portion of the ring finger. In addition, a small motor branch of the median nerve supplies the thenar muscles, which are responsible for lifting the thumb into opposition with the fingers.
Carpal tunnel syndrome describes numerous clinical signs and symptoms resulting from pressure on the median nerve inside the carpal tunnel. The typical etiology is increased pressure within the carpal tunnel, which interferes with the function of the median nerve. The patient experiences numbness and tingling in the fingers, together with pain that may radiate as far as the shoulder or base of the neck. Other symptoms include: Impaired grasping ability, due to sensory deprivation from the fingers; Loss of sleep from pain and numbness in the hand; and weakness or atrophy of the thenar muscles.
The pathology generally results from a swelling of the synovial membranes, which is often idiopathic. Carpal tunnel syndrome can also be caused by pressure on the median nerve from rheumatoid arthritis or edema in the final trimester of pregnancy.
Many instances of carpal tunnel syndrome can be treated conservatively, typically with a resting splint and cortisone injection into the carpal tunnel. However, if symptoms persist and/or reoccur, or if the patient has severe sensory deficit or loss of functions in the thenar muscles, then surgical decompression of the nerve by release of the transverse carpal ligament is often indicated.
Currently, surgical decompression is accomplished by a longitudinal incision paralleling the thenar crease. The incision is carried down through the skin, subcutaneous fat, and palmar fascia to divide the palmaris brevis muscle and then the transverse carpal ligament. Although the carpal tunnel is inspected, most cases do not require any surgical treatment within the carpal tunnel, other than the division of the ligament. Thereafter, the skin is sutured and the patient is splinted for approximately three weeks. A typical surgery requires approximately 20-25 minutes, including the dressing, and is performed as an outpatient procedure.
A patient whose occupation does not require extensive use of the hands can generally return to work within a few days, although writing may be difficult if the dominant hand is involved. However, in the frequent cases where the syndrome is occupationally related, i.e., where Workmen's Compensation is involved, the patient is usually disabled for six to eight weeks. If the patient is a manual laborer, two or three months may pass before a return to gainful employment. This postoperative morbidity is primarily due to persistent tenderness in the palm as the scar tissue matures. Most patients experience tenderness in the heel of their hand for four to six months following the surgery.
Previously, a few surgeons would release the carpal tunnel by inserting scissors through a transverse incision proximal to the carpal tunnel. The blind release by division of the ligament would then proceed from the proximal to the distal end. When successful, this technique decompresses the median nerve without scaring the heel of the patient's hand, significantly decreasing postoperative pain and morbidity.
However, transverse incision and blind release is not advisable, due to the risk of incomplete release of the carpal tunnel, or injury to the superficial arterial arch or the median nerve. The superficial palmar arterial arch lies just distal to the distal portion of the carpal ligament. The motor branch of the median nerve, which controls thumb opposition, is typically on the distal radial extent of the carpal tunnel, although anomalies can allow it to penetrate the carpal ligament in any of a number of positions and be subject to injury during blind release procedures.
Thus, it is also considered desirable to provide a surgical method and instrument for carpal tunnel release which reduces postoperative pain and morbidity while minimizing the risk of injury to neural or vascular tissue surrounding the carpal ligament.